This invention relates to compositions useful for curing polyurethane prepolymers, to process for preparing same, and to curable compositions made by mixing the resulting curing agent compositions with isocyanato-terminated prepolymers.
It is known that compositions having utility for curing polyurethane prepolymers can be made by forming a mixture of an inert organic liquid and particles of a complex of 4,4'-methylenedianiline (MDA) and a salt. However, the compositions of this type shown in the prior art have not been entirely satisfactory for many applications. For example, they have had one or more of such drawbacks as (a) too expensive to produce due to the need for subsequent operations to reduce particle size, and (b) poor shelf life of the curing agent/prepolymer mixtures as indicated by their tendency to undergo an undue increase in viscosity during storage. There is a real need in the art for a curing agent which forms mixtures with prepolymers having improved shelf life at room temperature and slightly above, and having the ability to cure rapidly at a suitable elevated temperature to form well-cured polyurethane products.